It is known that the perfluoropolyethers impart a marked hydrophobic property to the surface of materials to which they are applied.
Furthermore, the perfluoropolyethers have a high Bunsen coefficient for the air gas components, wherefore they permit a good penetration of the air through the surface of the treated materials.
These properties render the perfluoropolyethers interesting as liquids suitable for protecting building works and, in general, structures and articles manufactured from stones, marble, cement, tiles or wood from atmospheric agents. Such action is the more appreciated as the protection is reversible, being based on the deposition of a thin liquid layer onto the article surface, such layer being also removable, if necessary.
Furthermore, the low refraction index of the perfluoropolyethers, which corresponds to a value of about 1.3, measured at 20.degree. C. by the light of a sodium lamp, enables the treated article to retain its original appearance, avoiding optical interference phenomena which lead to an alteration of the colors.
The use of the aforesaid perfluoropolyethers has been described in European Pat. No. 59,100.
The perfluoropolyethers indicated by the above-cited prior art were of the type with "neutral" end groups, i.e., consisting of perfluoroalkyl groups which are chemically highly inert.
It was observed that the presence of porosity in the material to be protected leads to the phenomenon of a slow absorption of the perfluoropolyether of the type used so far, such phenomenon causing a more or less slow migration, depending on the type of porosity of the material of the protective liquid towards the innermost layers of the manufactured structures. That results in a lower effectiveness, in the long run, of the protection of the outermost areas of the treated structure. While on particular materials, such as, e.g., sandstones, such diffusion effect towards the inside is sufficiently slow as to provide protection stability for a long time, in other cases, for example in tiles, such phenomenon causes a decrease in the protective action at the surface as to require, after certain periods of time, further surface treatments, being, however, understood that the protection of the underlying layers remains sufficient to considerably slacken the alteration phenomena.